Since the advent of the acousto-optically Q-switched laser described in the U.S. Pat. No. 3,725,812, to Warner C. Scott, efforts have been made to increase the energy of the laser output pulses, as is desirable in many laser applications.
The laser described in the above-mentioned Scott patent utilizes a highly effective Q-switching technique, permitting very large buildups of population inversion level in the lasing rod. When the switch is turned on, raising the Q of the laser cavity by deflecting radiation at the Bragg angle to a feedback mirror, lasing action occurs in the system, accompanied by a large release of laser energy. One of the limiting factors in the amount of energy that could be present in the output pulse of such lasers has been the presence of dielectric optical coatings on various elements of the system.
It should be borne in mind that we are speaking of energies of the order of magnitude of 10-100 megawatts per square centimeter. At such energy levels, the optical coatings on mirror elements tend to be destroyed. The same is true of the anti-reflective coatings commonly present on the surface of the laser rod to prevent reflections and insure that the desired light energy enters the rod to establish and sustain lasing action.
Furthermore, when the laser rod is so highly pumped, to obtain output pulse energies in this range, the population inversion level is so high that, after the desired pulse is taken out, there is sufficient residual population inversion in the rod that a random emission in the cavity, upon entering the rod in nearly the axial direction, may create an undesired second laser output pulse.
Finally, in certain laser applications such as bomb guidance, it would be desirable to have a laser functioning at selectively variable wavelengths.
Accordingly, it is a feature of the present invention to provide a laser eliminating the problems associated with previously used optical coatings without the introduction of additional optical components, such as reflectors and beam splitters.
It is a further feature of the invention to provide increased output energy, by minimizing the possibility of unintended second output pulses, which usually limit the useful single pulse output energy of these lasers.
It is still another feature of the invention to provide a selectively variable laser output wavelength.
Other features and advantages of the invention will be apparent to persons skilled in the art from consideration of this specification, including the claims and drawings.